Large quantities of body-fluid samples, in particular blood but also urine and other body fluids, are tested in laboratories. These fluids are contained in sample tubes from which sub-quantities are removed with the aid of pipetting devices in order that one or more analyses can be carried out. This takes place essentially automatically. The main problem here is positive identification. It is, of course, necessary to be sure that the analysis data are assigned to the correct sample, and thus to the correct patient.
For this purpose, it is known for the tubes to be provided with an automatically readable marking, e.g. a bar code. In the case of a previously known apparatus, the tubes are arranged one behind the other in a row in a drawer-like frame and are pushed into the apparatus, the individual markings being identified by an identification device during the push-in operation by virtue of said device reading the bar code. Such a device cannot be 100% reliable since the frames with the tubes may possibly be pushed in incorrectly or it could be possible for a tube to be exchanged after the push-in operation, this exchange not being detected by the apparatus since the identification has already taken place beforehand, namely during the operation for pushing the row of tubes in.
In the case of another apparatus, at the same time as the identification takes place, the fluid from the sample tube is introduced, with the aid of a pipette, into a further tube, which is located in a closed carousel. This ensures positive identification since it is not possible for any sample tubes to be removed from the carousel. The problem which does arise, however, is that two sample tubes have to be used for each body fluid, and this signifies an increase in waste.
It is also known for the tubes to be arranged in the form of a chain and, in this case, for that part of the chain in which the sample removal takes place to be guided through a closed-top chamber such that it is not possible for any tube to be removed. The identification takes place during sample removal by the pipette, thus ensuring positive identification. However, such a chain is complicated, in particular if a number of analyses are to be carried out on the same sample. If the analysis establishes that, due to critical values, a further analysis should be carried out, then the corresponding tube is no longer located at the sample-removal location and so has to be inserted manually again at the beginning of the chain. This is also very complicated.
Finally, it is known for the tubes to be inserted in a carousel or rotor, the identification taking place at the time of sample removal. Although positive identification is ensured, it is necessary, once the measurements have been completed, for the tubes to be removed individually from the rotor or for the rotor, which is positioned on a spindle, to be lifted out in order for the tubes to be disposed of. This is very complicated. There is also the problem of exchange having to take place once the analyses have been completed. If the operator is otherwise occupied at this point, which will usually be the case, then the apparatus remains at a standstill for some time until it is noticed that new tubes have to be inserted. This amount of time wasted means that the apparatus is utilized less economically and it may be necessary for overtime to be worked in order for the day's analyses to be completed as planned.